Operators of mines are constantly searching for ways to reduce the costs associated with mined products. One of the most significant costs in operating a mine is transporting the mined material from the ore face to a processing plant. This is exacerbated when the mined payload is of low grade, that is, the desired mineral or metal is only a small percentage by weight and/or volume of the mined ore so that substantial amounts of ore have to be handled to extract a small percentage of desired material. A further problem that occurs is where the ore has to be handled several times.
There are several ways that ore can be transported from the ore face to the processing plant, depending on the type and configuration of the mine.
Underground mines typically have a central lifting or winding shaft to bring the mined ore to the surface. These shafts require a dedicated receival point. To get the ore to that point mines typically have a dedicated rail system that is level and route specific. Underground mine haulage or dump trucks are used to transport the ore from various mining levels both above and below the rail haulage level to the dedicated rail system that then transports the ore to the lifting shaft receival point. The trucks are always a single unit that is either rigid or pivot steer. This type of arrangement has a number of distinct disadvantages.
The dump trucks cause a significant amount of hot air per ton of ore hauled to be exhausted into the mine. Cold ventilation air has to be continually pumped into the mine via ventilation shafts, and one of the major costs in establishing underground mines is the construction and drilling of ventilation shafts. Because of the limitation of currently known dump trucks, the time that they can operate underground is limited, particularly due to excess heat they produce. To reduce the heat, the dump trucks have to move relatively slowly.
A railway system, especially one underground, is relatively expensive to install and operate due to the cost of acquiring the locomotive and installing the fixed railway system and the associated maintenance costs. Furthermore the underground railway system being route-specific is not flexible to changes in route without incurring the expense of installing additional railway tracks. As each new mining area opens, it is necessary to incur the cost of installing new track for the railway system, or use the dump trucks as described above whose efficiency decreases with increasing distances they have to travel.
The central lifting or winding shaft is quite expensive, the cost running into tens of millions of dollars and is of a fixed location. As the mine expands the distance from the ore face to the central shaft becomes important in the cost of operating the mine.
In some instances mines have utilized conveyor belts instead of the railway system and/or the lifting shaft. The difficulty with conveyor belts is that once again they are route specific, are quite expensive to install and maintain. Miners are also concerned that the belts may catch fire that would starve the area of oxygen.
In some instances the dump trucks may be used to transport the ore directly above ground. Because of the limitations described above, especially low speed and the heat they produce and with the inclination within underground mines generally being constant, the depth of a mine that can be realistically accessed by these dump trucks is therefore limited, typically to a depth of hundreds of meters.
When the ore has been transported to the surface, or in the case of an above ground mine, it is then necessary to transport the ore to a central processing plant.
One of the ways that this may be accomplished is by using conventional off-highway dump trucks that can either be a single rigid, pivot steer unit or an articulated vehicle consisting of a very short wheelbase earthmoving type or tractor unit coupled to a single hauled or carrying unit and virtually job specific. These units are designed to be a link in the chain of the actual mining, digging or producing the/any product. Their main function is to move product literally from the ore face to a receival point through the shortest possible distance are not route-specific. The shorter the route the more economical they are, conversely, their tonne of ore transported per distance costs increase dramatically over longer routes. They are therefore not suitable for hauling ore great distances, thereby limiting the distance that ore can be transported at a reasonable cost. As such, these trucks are not suitable when there may be satellite mines, that is, mines that are some distance away from the processing plant. In particular, these trucks have never been designed to be a transportation system for various reasons including the following:                (a) Their axle loadings are extreme and require appropriate roading and bridging. Wheeled or articulated dump trucks with large tires carry a significant loading per axle, up to 33 tons per axle.        (b) These types of trucks being designed for hauling loads over relatively short distances and rough terrain are therefore designed with relatively large tires for relatively slow speed operation and are relatively expensive to operate and maintain due to fuel and tire costs.        (c) They produce too much heat in both their drive trains and tires. Furthermore they have poor power-to-weight ratios and low operating efficiencies.        (d) Their mass requires a large cross-section both in height and width.        (e) Their discharge methods are either: direct end tip (non captive) where the center of gravity is always raised, or bottom dump in the single articulated hauling vehicle that keeps the center of gravity down but is discharge captive.        
An alternate way of transporting the ore to a central processing plant includes conventional type transportation system such as conveyor belts and rail systems, both routes being captive. Problems with these have been discussed above.
Another way of transporting the ore is using highway type road vehicle combinations or multi-combination vehicles. These vehicles are limited by their horsepower, tractive or braking efforts or capacities, manufacturers ratings of various componentry, directional stability behavior, swept path characteristics, gradability and startability.
As a result, currently known systems for the extraction of ore from mines set limits on the commercial usefulness of mines simply due to the cost of transporting the ore.
As discussed above multi-combination vehicles, such as over-the-road vehicles are known and include a truck coupled to a plurality of trailers and converter dollies. Until recently these vehicles have included a single power source, generally a diesel engine, with the vehicles being limited to a payload of some 170 tonnes, and a gradient not exceeding 5%. These multicombination vehicles, commonly referred to as “road-trains” have been in use for some time, particularly in Australia, for the purpose of hauling mined products, or the commodities of other industries, over aboveground roadways. Conventional aboveground road-trains are typically designed for use at relatively high speed and on relatively flat ground. They are limited by their horse power, tractive or braking efforts and their capacities that are defined by manufacturers ratings, directional stability behaviour, swept path characteristics, gradability and startability. Accordingly they have limited uses for operation in mines.
The location of the mechanical couplings between each adjacent pair of vehicles in a multi-combination vehicle as described above is positioned to maintain the side-to-side sway, or yaw, of the last vehicle within acceptable limits for aboveground, over-the-road applications, but is not compatible for operation within an underground mine due to the relatively low operating speeds as well as the relatively narrow tunnels and small radius bends experienced in underground mines.
Specially configured multi-combination vehicles have been developed recently which have a significantly reduced swept path width as compared to conventional aboveground road-trains. This enables these vehicles to be used to transport various payloads such as mined ores, over the roadways existing in an underground mine. U.S. Pat. No. 6,062,801 issued on May 16, 2000 and U.S. Pat. No. 6,361,269 issued on Mar. 26, 2002, each expressly incorporated by reference herein in its entirety, describe these specially configured multi-combination vehicles which may be used in underground mines. The vehicles can operate in a tunnel system with restricted height, width, swept paths and directional path complying with a predetermined behaviour pattern obviating the need for the rail or conveyor system.
Even after the advent of the foregoing specially configured multi-combination vehicles, various operational problems remained to be solved with regard to the transport of mined ores, in both underground and aboveground applications. For instance, due to the heavy loads of the road-train combination, the traction provided by the powered wheels of a road-train, usually provided to two rear axles, was insufficient to satisfactorily negotiate the gradients associated with the declines providing ingress and egress to and from some underground mines. Alternatively these declines into underground mines would have to be constructed at a much gentler slope leading to excessively long tunnels. In addition, the relatively low speed of the road trains underground due to the size of the tunnels and safety considerations result in road-trains travelling underground for a significant length of time, even up to an hour in some cases. This places strain on the road-train cooling system that is typically designed for aboveground road-trains travelling at significant speeds, generally around 80 km/h and the engines are prone to overheating.
Also, before the introduction of multi-combination vehicles incorporating a power trailer (i.e., one having a source of motive power), which are subsequently discussed in detail, multi-combination vehicles for dedicated road haulage therefor such as mineral concentrate haulage operated at a 170 tonne payload, as noted previously. However, there is a practical limit to the payload of the multi-combination vehicle with a single truck. Since the cost of haulage is determined mainly on weight, if one can increase the total haulage that can be moved by a single vehicle that does not require additional operators, the cost benefit is substantial especially. This is especially so if ore can be hauled directly from within a mine to a processing plant without needing to be reloaded onto another transport system.
In order to further improve multi-combination vehicles and provide even greater advantages to the operators using these vehicles, multi-combination vehicles have been developed which utilize a truck and an additional motive power source advantageously located within the chassis of a trailer and including a unique cooling system that enables operation of the multi-combination vehicle at low speeds, on steeper gradients and with a greater payload than previously known. International Patent Application No. PCT/AU01/01154, expressly incorporated by reference herein in its entirety, discloses a multi-combination vehicle including a power trailer having an engine that overcomes the foregoing problems of traction and cooling of such multi-combination vehicles. International Patent Application No. PCT/AU01/01568, also expressly incorporated by reference herein in its entirety, discloses various features that may be incorporated in the drive trains of multi-combination vehicles of this type. These multi-combination vehicles having the ability to transverse different mining levels have removed the need for conventional dump truck haulage from the ore face to the rail head, and have also enabled the vehicle to haul ore directly from the ore face from any level underground via an access tunnel directly to a processing plant eliminating the need for the lifting shaft. Furthermore, these types of multi-combination vehicles coupled with specifically configured power trailers, typically B-double trailers, can be used above ground to transport ore directly to a processing plant eliminating the need for other dump trucks, increasing the total payload from some 170 tonnes to 270 tonnes whilst staying within the manufacturers rating and at the same time increasing the general behavior pattern creating a safer multi-combination vehicle.
Use of a multi-combination vehicle using a truck and a power trailer provides a further significant advantage over conventional single-engine dump trucks, as well as multi-combination vehicles having only a truck, in that even if the truck or power trailer engine or transmission were to fail, the alternative engine and transmission can be used to at least move the multi-combination vehicle out of the way or even bring it to the surface for analysis and repair. As known in the art, in the event of engine and/or transmission failure it is more than a simple exercise to retrieve a single-engine dump truck from the depths of an underground mine that is then blocking the underground road for use by other trucks. A similar problem may exist with multi-combination vehicles powered only by a single truck, or in some instances a single prime mover.
One of the problems in a multi-combination vehicle having two engines and transmissions is controlling them. International Patent Application No. PCT/AU02/00667, expressly incorporated by reference herein in its entirety, discloses a system for the control of multiple engines in a multi-combination vehicle including a power trailer having an engine, which overcomes the foregoing problems of controlling multiple engines. International Patent Application No. PCT/AU02/00668, also expressly incorporated by reference herein in its entirety, discloses a system for the control of multiple transmissions in a multi-combination vehicle including a power trailer having an engine, which overcomes the foregoing problems of controlling multiple transmissions.
A difficulty in a load carrying vehicles and especially in relation to multi-combination vehicles as described above is that the terminal speed of the vehicle has to be a carefully controlled parameter especially when it is carrying a load or descending into a mine. If the vehicle is travelling too fast down into a mine the brakes overheat and become ineffective. The problem is even greater in the case where there are multi-combination vehicles and where the power trailer effectively keeps pushing the truck.
The driver of the vehicle may select engine braking, when be experience they think that the vehicle is travelling at a too fast velocity. This relies on the operating skill of the driver and is affected by driver fatigue and concentration. Where engine braking is not applied in time, the vehicle can run out of control potentially damaging the vehicle, the mine and threaten the life of people in the vicinity. In fact, runaway vehicles are one of the more common reasons for damage and disruption in a mine. This problem is exacerbated by the fact that in currently known engine braking systems the engine braking will only apply when the throttle is not engaged. If the driver, for whatever reason, is still applying a throttle even if they select engine braking it will not be activated. In the worst-case scenario where the driver looses consciousness and is still applying a throttle the vehicle will not stop or slow down of its own accord.
The present invention seeks to redress the above-mentioned problems by providing for a vehicle engine braking system wherein the throttle is inhibited and engine braking applied once the vehicle speed reaches a pre-determined velocity. The present invention further seeks to redress the aforementioned problems by providing for a system for the velocity control of a multi-combination vehicle where the operator can select the relative braking applied by the power trailer and the truck wherein the trailer always applied engine braking that is equal to or greater than that supplied by the truck. The present invention seeks even further to redress the aforementioned problems by providing for a variable velocity engine braking system wherein once the speed of the vehicle falls below the pre-determined threshold, throttle control is enabled whilst engine braking is turned off.
The inventor is unaware of any vehicle including a multi-combination vehicle, whether it is for above ground or underground use of the type just described, which is capable of applying engine braking only dependant on the speed of the vehicle. The inventor is further unaware of any multi-combination vehicle where the operator can select the relative engine braking of the truck and power trailer.
In view of the foregoing disadvantages and limitations associated with known load-carrying vehicles, a commercial need exists for an improved load-carrying vehicle and vehicle combination for use both aboveground and in underground mines that overcomes at least some of the abovementioned problems or provides the public with a useful alternative.
It is therefore an object of the present invention to provide a braking system for a vehicle that overcomes the above noted drawbacks and disadvantages associated with prior art vehicle braking systems.
It is another object of the present invention to provide a braking system for velocity dependent controlled braking for a vehicle.
It is another object of the present invention to provide a braking system for velocity dependent controlled braking system for a multi-combination vehicle having a powered truck and a powered trailer.
It is yet another object of the present invention to provide a braking system for a vehicle that includes a manual override control that enables an operator of the vehicle to apply variable engine braking independent of the vehicle speed.